1. Field of the Invention
The present invention relates to a rubber adhesive for bonding rubber to an adherend.
2. Description of the Prior Art
There are two common methods for bonding rubber and metal to each other as illustrated in FIGS. 2 and 3 in the accompanying drawing. According to the first method shown in FIG. 2, a primer (23) composed mainly of phenolic resin is applied to the adherend surface (21a) of a metal (21). After the primer (23) has been dried, a rubber adhesive (24) composed mainly of chlorinated rubber is applied to the dried primer. On the rubber adhesive (24) is placed vulcanized or unvulcanized rubber (25), which is thereafter pressed with heating, whereby bonding is made between metal (21) and rubber (25). According to the second method shown in FIG. 3, an adhesive (26) containing both the above-mentioned primer and the rubber adhesive is applied directly to the adherend surface (21a) of the metal substrate (21), followed by drying. On the dried adhesive is placed vulcanized or unvulcanized rubber (25), which is thereafter pressed with heating in the same manner as in the first method, whereby bonding is made between metal (21) and rubber (25).
The above-mentioned two common methods that employ the rubber adhesive (24) or (26) do not provide bonding between rubber (25) and metal (21) with sufficiently high adhesive strength. This holds true particularly in the case where IIR (butyl rubber), Cl-IIR (chlorinated butyl rubber), or EPDM (ethylene-propylene rubber) is to be bonded. In addition, for these kinds of rubber, the common methods require a long time for the pressing and heating steps.